Conventional thermal management in high power semiconductor devices includes a diamond heat spreader mounted on a copper heat sink that is subsequently cooled by chilled water or glycol. The diamond heat spreader can be a single-crystal or polycrystalline.
Single-crystal diamond is an effective heat spreader due to its high thermal conductivity. For example, single-crystal diamonds can be used as external heat spreaders or intracavity heat spreaders. Problems arise, however, because it is difficult to obtain a desirable low surface roughness. The low surface roughness is required to ensure a direct bonding of single-crystal diamond with high power devices without generating air gaps or voids at the interface. In addition, single-crystal diamonds are expensive.
Polycrystalline diamond is several orders of magnitude cheaper than single-crystal diamond, yet with comparable thermal conduction. Polycrystalline diamonds are often formed by chemical vapor deposition (CVD), which provides undesirable surface roughness. It is thus also a challenge for polycrystalline diamonds to obtain a desirable low surface roughness because polycrystalline diamonds have a similar hardness as single-crystal diamonds. Large voids can be generated at the interface of the polycrystalline diamonds and the high power devices. The poor thermal conduction due to the voids generated at the interface significantly hinders efficient heat transfer.
To address the surface roughness issues of the polycrystalline diamonds, conventional methods use capillary fluid (water or ethanol) and indium alloy solder to bond polycrystalline diamonds to high power devices. However, there is no efficient wetting of the rough surface of the polycrystalline diamonds for either the capillary fluid or the indium alloy solder. Voids are still generated at the interface of the diamonds and the high power devices.
Thus, there is a need to overcome these and other problems of the prior art and to provide methods for forming and integrating a diamond heat spreader with a heat source without generating voids at their interface.